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data-v-531573d4>BOM是什么</p></a><a class="link" href="/js/31.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>window 对象</p></a><a class="link" href="/js/32.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>Navigator 对象和Screen 对象</p></a><a class="link" href="/js/33.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>History对象和Location对象</p></a><a class="link" href="/js/34.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>表单和FormData 对象</p></a><a class="link" href="/js/35.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>Storage接口</p></a><a class="link" href="/js/36.html" data-v-59eaa146 data-v-531573d4><p class="link-text" data-v-531573d4>节流和防抖</p></a><!--]--></section></div><!--]--><!--[--><!--]--></nav></aside><div id="VPContent" class="VPContent has-sidebar" data-v-23306c50 data-v-790151bc><div class="VPContentDoc has-aside has-sidebar" data-v-790151bc data-v-4fe9b7bd><div class="container" data-v-4fe9b7bd><div class="aside" data-v-4fe9b7bd><div class="aside-container" data-v-4fe9b7bd><!--[--><!--]--><div class="VPContentDocOutline" data-v-4fe9b7bd data-v-aa0e2252><div class="outline-marker" data-v-aa0e2252></div><div class="outline-title" data-v-aa0e2252>On this page</div><nav aria-labelledby="doc-outline-aria-label" data-v-aa0e2252><span id="doc-outline-aria-label" class="visually-hidden" data-v-aa0e2252>Table of Contents for current page</span><ul class="root" data-v-aa0e2252><!--[--><li style="" data-v-aa0e2252><a class="outline-link" href="#_10-1-math-abs" data-v-aa0e2252>10.1 Math.abs()</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_10-2-math-max-，math-min" data-v-aa0e2252>10.2 Math.max()，Math.min()</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_10-3-math-floor-，math-ceil" data-v-aa0e2252>10.3 Math.floor()，Math.ceil()</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_10-4-math-round" data-v-aa0e2252>10.4 Math.round()</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_10-5-math-random" data-v-aa0e2252>10.5 Math.random()</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_11-1-概述" data-v-aa0e2252>11.1 概述</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_11-2-实例属性" data-v-aa0e2252>11.2 实例属性</a><!----></li><li style="" data-v-aa0e2252><a class="outline-link" href="#_11-3-实例方法" data-v-aa0e2252>11.3 实例方法</a><!----></li><!--]--></ul></nav></div><!--[--><!--[--><!--[--><div><a class="sponsors-aside-text" href="/">联系客服</a><img src="/images/qrcode.png"></div><!--]--><!--]--><!--]--><div class="VPCarbonAds" data-v-4fe9b7bd><img src="/logo.svg" alt="" srcset=""></div><!--[--><!--[--><!--[--><h1 class="tagline" data-v-3916b2f0><span class="accent" data-v-3916b2f0>Bin</span><br data-v-3916b2f0>QQ - 1974892005 </h1><!--]--><!--]--><!--]--></div></div><div class="content" data-v-4fe9b7bd><!--[--><!--]--><main data-v-4fe9b7bd><div style="position:relative;" class="vt-doc js" data-v-4fe9b7bd><div><h1 id="_10-math对象" tabindex="-1">10.Math对象 <a class="header-anchor" href="#_10-math对象" aria-hidden="true">#</a></h1><p><code>Math</code>是 JavaScript 的原生对象，提供各种数学功能。该对象不是构造函数，不能生成实例，所有的属性和方法都必须在<code>Math</code>对象上调用。</p><p><code>Math</code>对象提供以下一些静态方法。</p><ul><li><code>Math.abs()</code>：绝对值</li><li><code>Math.ceil()</code>：向上取整</li><li><code>Math.floor()</code>：向下取整</li><li><code>Math.max()</code>：最大值</li><li><code>Math.min()</code>：最小值</li><li><code>Math.round()</code>：四舍五入</li><li><code>Math.random()</code>：随机数</li></ul><h2 id="_10-1-math-abs" tabindex="-1">10.1 Math.abs() <a class="header-anchor" href="#_10-1-math-abs" aria-hidden="true">#</a></h2><p><code>Math.abs</code>方法返回参数值的绝对值。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">abs</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">abs</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h2 id="_10-2-math-max-，math-min" tabindex="-1">10.2 Math.max()，Math.min() <a class="header-anchor" href="#_10-2-math-max-，math-min" aria-hidden="true">#</a></h2><p><code>Math.max</code>方法返回参数之中最大的那个值，<code>Math.min</code>返回最小的那个值。如果参数为空, <code>Math.min</code>返回<code>Infinity</code>, <code>Math.max</code>返回<code>-Infinity</code>。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">max</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">min</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -1</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">min</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// Infinity</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">max</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// -Infinity</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><h2 id="_10-3-math-floor-，math-ceil" tabindex="-1">10.3 Math.floor()，Math.ceil() <a class="header-anchor" href="#_10-3-math-floor-，math-ceil" aria-hidden="true">#</a></h2><p><code>Math.floor</code>方法返回小于或等于参数值的最大整数（地板值）。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -4</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><code>Math.ceil</code>方法返回大于或等于参数值的最小整数（天花板值）。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">ceil</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 4</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">ceil</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -3</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>这两个方法可以结合起来，实现一个总是返回数值的整数部分的函数。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">ToInteger</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">x</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#FFCB6B;">Number</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">0</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">?</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">ceil</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;">) </span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">x</span><span style="color:#F07178;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3.5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3.8</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">3.2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -3</span></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">3.5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -3</span></span>
<span class="line"><span style="color:#82AAFF;">ToInteger</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">3.8</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -3</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p>上面代码中，不管正数或负数，<code>ToInteger</code>函数总是返回一个数值的整数部分。</p><h2 id="_10-4-math-round" tabindex="-1">10.4 Math.round() <a class="header-anchor" href="#_10-4-math-round" aria-hidden="true">#</a></h2><p><code>Math.round</code>方法用于四舍五入。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0.1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 0</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0.5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0.6</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 等同于</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#A6ACCD;">(x </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0.5</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>注意，它对负数的处理（主要是对<code>0.5</code>的处理）。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1.1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -1</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1.5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -1</span></span>
<span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">round</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1.6</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// -2</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h2 id="_10-5-math-random" tabindex="-1">10.5 Math.random() <a class="header-anchor" href="#_10-5-math-random" aria-hidden="true">#</a></h2><p><code>Math.random()</code>返回0到1之间的一个伪随机数，可能等于0，但是一定小于1。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">random</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// 0.7151307314634323</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>任意范围的随机数生成函数如下。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">getRandomArbitrary</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">min</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> max</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">random</span><span style="color:#F07178;">() </span><span style="color:#89DDFF;">*</span><span style="color:#F07178;"> (</span><span style="color:#A6ACCD;">max</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">min</span><span style="color:#F07178;">) </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">min</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">getRandomArbitrary</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1.5</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">6.5</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 2.4942810038223864</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>任意范围的随机整数生成函数如下。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">getRandomInt</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">min</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> max</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">random</span><span style="color:#F07178;">() </span><span style="color:#89DDFF;">*</span><span style="color:#F07178;"> (</span><span style="color:#A6ACCD;">max</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">min</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">1</span><span style="color:#F07178;">)) </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">min</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">getRandomInt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 5</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>返回随机字符的例子如下。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">random_str</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">length</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#C792EA;">var</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">ALPHABET</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">ABCDEFGHIJKLMNOPQRSTUVWXYZ</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">ALPHABET</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abcdefghijklmnopqrstuvwxyz</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">ALPHABET</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">0123456789-_</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#C792EA;">var</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">str</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;font-style:italic;">for</span><span style="color:#F07178;"> (</span><span style="color:#C792EA;">var</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">i</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">;</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">i</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">length</span><span style="color:#89DDFF;">;</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">++</span><span style="color:#A6ACCD;">i</span><span style="color:#F07178;">) </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#C792EA;">var</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">rand</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">floor</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">Math</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">random</span><span style="color:#F07178;">() </span><span style="color:#89DDFF;">*</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">ALPHABET</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">length</span><span style="color:#F07178;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#A6ACCD;">str</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+=</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">ALPHABET</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#F07178;">(</span><span style="color:#A6ACCD;">rand</span><span style="color:#89DDFF;">,</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">rand</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">+</span><span style="color:#F07178;"> </span><span style="color:#F78C6C;">1</span><span style="color:#F07178;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#A6ACCD;">str</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">random_str</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;NdQKOr&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>上面代码中，<code>random_str</code>函数接受一个整数作为参数，返回变量<code>ALPHABET</code>内的随机字符所组成的指定长度的字符串。</p><h1 id="_11-string对象" tabindex="-1">11.String对象 <a class="header-anchor" href="#_11-string对象" aria-hidden="true">#</a></h1><h2 id="_11-1-概述" tabindex="-1">11.1 概述 <a class="header-anchor" href="#_11-1-概述" aria-hidden="true">#</a></h2><p><code>String</code>对象是 JavaScript 原生提供的三个包装对象之一，用来生成字符串对象。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> s2 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">new</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#89DDFF;">typeof</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#676E95;font-style:italic;">// &quot;string&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">typeof</span><span style="color:#A6ACCD;"> s2 </span><span style="color:#676E95;font-style:italic;">// &quot;object&quot;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">s2</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">valueOf</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// &quot;abc&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>上面代码中，变量<code>s1</code>是字符串，<code>s2</code>是对象。由于<code>s2</code>是字符串对象，<code>s2.valueOf</code>方法返回的就是它所对应的原始字符串。</p><p>字符串对象是一个类似数组的对象（很像数组，但不是数组）。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">new</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// String {0: &quot;a&quot;, 1: &quot;b&quot;, 2: &quot;c&quot;, length: 3}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">new</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))[</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">] </span><span style="color:#676E95;font-style:italic;">// &quot;b&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>上面代码中，字符串<code>abc</code>对应的字符串对象，有数值键（<code>0</code>、<code>1</code>、<code>2</code>）和<code>length</code>属性，所以可以像数组那样取值。</p><p>除了用作构造函数，<code>String</code>对象还可以当作工具方法使用，将任意类型的值转为字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#FFCB6B;">String</span><span style="color:#A6ACCD;">(</span><span style="color:#FF9CAC;">true</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;true&quot;</span></span>
<span class="line"><span style="color:#FFCB6B;">String</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;5&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>上面代码将布尔值<code>true</code>和数值<code>5</code>，分别转换为字符串。</p><h2 id="_11-2-实例属性" tabindex="-1">11.2 实例属性 <a class="header-anchor" href="#_11-2-实例属性" aria-hidden="true">#</a></h2><p><strong>String.prototype.length</strong></p><p>字符串实例的<code>length</code>属性返回字符串的长度。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">length </span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h2 id="_11-3-实例方法" tabindex="-1">11.3 实例方法 <a class="header-anchor" href="#_11-3-实例方法" aria-hidden="true">#</a></h2><p><a href="https://www.w3school.com.cn/js/js_string_methods.asp" target="_blank" rel="noopener noreferrer">W3C JavaScript 字符串方法</a></p><blockquote><p>ES6中的字符串新方法</p><p><strong>String.prototype.padStart(maxLength, fillString=&#39;&#39;)</strong> 或 **String.prototype.padEnd(maxLength, fillString=&#39;&#39;)**来填充字符串；</p></blockquote><table><thead><tr><th>方法</th><th>作用</th></tr></thead><tbody><tr><td></td><td></td></tr><tr><td>length</td><td>获取字符串的长度</td></tr><tr><td>charAt()</td><td>根据索引获取指定的字符</td></tr><tr><td>charCodeAt()</td><td>根据索引获取指定的字符编码</td></tr><tr><td>String.fromCharCode()</td><td>根据字符编码获取字符</td></tr><tr><td>indexOf()</td><td>查找字符/子字符串在大字符串中<strong>第一次出现的位置，找到了返回下标，找不到返回-1；</strong></td></tr><tr><td>lastIndexOf()</td><td>从一个字符串中检索指定内容 <br> 如果找到该内容，则会返回其第一次出现的索引，如果没有找到则返回-1。 <br>可以指定一个第二个参数，来表示开始查找的位置 indexOf()是从前向后找 lastIndexOf()是从后向前找</td></tr><tr><td>slice(start,[end])</td><td>可以从一个字符串中截取指定的内容，并将截取到内容返回，不会影响原变量 <br>参数： <br> 第一个：截取开始的位置（包括开始） <br> 第二个：截取结束的位置**（不包括结束）** <br> 可以省略第二个参数，如果省略则一直截取到最后 <br> 可以传负数，如果是负数则从后往前数</td></tr><tr><td>substr()</td><td>和slice()基本一致，不同的是它第二个参数不是索引，而是截取的数量</td></tr></tbody></table><table><thead><tr><th>方法</th><th>功能</th></tr></thead><tbody><tr><td><code>charAt()</code></td><td>得到指定位置字符</td></tr><tr><td><code>substring()</code></td><td>提取子串</td></tr><tr><td><code>substr()</code></td><td>提取子串</td></tr><tr><td><code>slice()</code></td><td>提取子串</td></tr><tr><td><code>toUpperCase()</code></td><td>将字符串变为大写</td></tr><tr><td><code>toLowerCase()</code></td><td>将字符串变为小写</td></tr><tr><td><code>indexOf()</code></td><td>检索字符串</td></tr><tr><td><code>includes()</code></td><td>判断子字符串是否存在</td></tr><tr><td><code>lastIndexOf()</code></td><td>从末尾检索字符串</td></tr><tr><td><code>trim()</code></td><td>删除首尾空格</td></tr><tr><td><code>trimStart()</code></td><td>删除首部空格</td></tr><tr><td><code>trimEnd()</code></td><td>删除尾部空格</td></tr><tr><td><code>match()</code></td><td>匹配子字符串</td></tr><tr><td><code>search()</code></td><td>搜索子字符串的第一次出现位置</td></tr><tr><td><code>replace()</code></td><td>替换匹配的子字符串</td></tr><tr><td><code>split()</code></td><td>分割字符串变成数组</td></tr><tr><td><code>concat()</code></td><td>连接两个字符串</td></tr></tbody></table><h3 id="_11-3-1-charat-方法" tabindex="-1">11.3.1 charAt() 方法 <a class="header-anchor" href="#_11-3-1-charat-方法" aria-hidden="true">#</a></h3><p><code>charAt()</code> 方法可以得到指定位置的字符。</p><p>字符串中的每个字符都按顺序编号，编号从 0 开始。</p><table><thead><tr><th><code>&quot;</code></th><th>我</th><th>喜</th><th>欢</th><th>J</th><th>S</th><th>,</th><th>我</th><th>也</th><th>喜</th><th>欢</th><th>N</th><th>O</th><th>D</th><th>E</th><th><code>&quot;</code></th></tr></thead><tbody><tr><td></td><td>0</td><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td><td>10</td><td>11</td><td>12</td><td>13</td><td></td></tr></tbody></table><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;我&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;，&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">11</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// &quot;O&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">99</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// &quot;&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// &quot;&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>这个方法完全可以用数组下标替代。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;b&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">[</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">] </span><span style="color:#676E95;font-style:italic;">// &quot;b&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>如果参数为负数，或大于等于字符串的长度，<code>charAt</code>返回空字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">charAt</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="_11-3-2-substring-、substr-和-slice-方法" tabindex="-1">11.3.2 substring()、substr() 和 slice() 方法 <a class="header-anchor" href="#_11-3-2-substring-、substr-和-slice-方法" aria-hidden="true">#</a></h3><p><strong>（1）<code>substring(a, b)</code> 方法得到从 a 开始到 b 结束（不包括 b 处）的子串</strong> <code>[a, b)</code></p><blockquote><p>编程语言的区间一般都是：左闭右开</p></blockquote><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">10</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">14</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;NODE&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">10</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">99</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;NODE&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;我喜欢J&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><blockquote><p>超出范围的部分，取到端点字符。</p></blockquote><ul><li>substring(a, b) 方法如果省略第二个参数，返回的子串会一直到字符串的结尾</li></ul><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;我也喜欢NODE&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>substring(a, b) 中，a 可以大于 b，数字顺序将自动调整为小数在前</li></ul><blockquote><p>应该没有人会这样用</p></blockquote><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substring</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>（2）<code>substr(a, b)</code> 中，将得到从 a 开始的长度为 b 的子串</strong></p><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substr</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>substr(a, b) 中，b 可以省略，表示到字符串结尾</li></ul><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substr</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS，我也喜欢NODE&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>substr(a, b) 中，a 可以是负数，表示倒数位置</li></ul><blockquote><p>倒数第一位为 -1，而不是 -0</p></blockquote><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">substr</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;NO&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><strong>（3）<code>slice(a, b)</code> 方法得到从 a 开始到 b 结束（不包括 b 处）的子串</strong></p><blockquote><p>slice：切片</p></blockquote><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">slice</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">5</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;JS&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>slice(a, b) 的参数 a 可以是负数（与 substring(a, b) 的区别）</li></ul><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">slice</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">4</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;NOD&quot;</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// (-4, -1)：从 倒数第4位 到 倒数第1位，不包括 倒数第1位</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>slice(a, b) 中，参数 a 必须小于参数 b，否则便会返回一个空字符串</li></ul><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">我喜欢JS，我也喜欢NODE</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">slice</span><span style="color:#A6ACCD;">(</span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="_11-3-3-touppercase-和-tolowercase-方法" tabindex="-1">11.3.3 toUpperCase() 和 toLowerCase() 方法 <a class="header-anchor" href="#_11-3-3-touppercase-和-tolowercase-方法" aria-hidden="true">#</a></h3><ul><li><code>toUpperCase()</code> 转为大写</li><li><code>toLowerCase()</code> 转为小写</li></ul><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">I Love You</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toUpperCase</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;I LOVE YOU&quot;</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">IMooc</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toLowerCase</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		    </span><span style="color:#676E95;font-style:italic;">// &quot;imooc&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><blockquote><p>注意：toUpperCase() 和 toLowerCase()，只是返回一个大小写格式，变量本身的值并没有改变。</p><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> str </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">I Love You</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(str</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toUpperCase</span><span style="color:#A6ACCD;">())</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// &quot;I LOVE YOU&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(str)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">				   </span><span style="color:#676E95;font-style:italic;">// &quot;I Love You&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">str </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> str</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">toUpperCase</span><span style="color:#A6ACCD;">()</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(str)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">				   </span><span style="color:#676E95;font-style:italic;">// &quot;I LOVE YOU&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div></blockquote><h3 id="_11-3-4-indexof-、includes-和lastindexof-方法" tabindex="-1">11.3.4 indexOf()、includes()和lastIndexOf() 方法 <a class="header-anchor" href="#_11-3-4-indexof-、includes-和lastindexof-方法" aria-hidden="true">#</a></h3><p><strong>(1) indexOf()</strong></p><p><code>indexOf()</code> 方法返回某个指定的字符串值在字符串中首次出现的位置</p><p>如果要检索的字符串没有出现，则返回 <code>-1</code></p><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">abcdebb</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">indexOf</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">b</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">abcdebb</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">indexOf</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">deb</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">	</span><span style="color:#676E95;font-style:italic;">// 3</span></span>
<span class="line"><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">abcdebb</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">indexOf</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">m</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span><span style="color:#A6ACCD;">		</span><span style="color:#676E95;font-style:italic;">// -1</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>(2) includes()</strong></p><p>ES6新增</p><p>includes(string) 此函数检查字符串<strong>是否包含子字符串</strong>，返回布尔值。</p><p>使用方法和indexOf一样</p><p><strong>(3) lastIndexOf()</strong></p><p><code>lastIndexOf</code>方法的用法跟<code>indexOf</code>方法一致，主要的区别是<code>lastIndexOf</code>从尾部开始匹配，<code>indexOf</code>则是从头部开始匹配。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">hello world</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">lastIndexOf</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">o</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 7</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>另外，<code>lastIndexOf</code>的第二个参数表示从该位置起向前匹配。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">hello world</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">lastIndexOf</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">o</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">6</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 4</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="_11-3-5-trim-、trimstart-、trimend-方法" tabindex="-1">11.3.5 trim()、trimStart()、trimEnd() 方法 <a class="header-anchor" href="#_11-3-5-trim-、trimstart-、trimend-方法" aria-hidden="true">#</a></h3><div class="language-javascript line-numbers-mode"><pre><code><span class="line"><span style="color:#676E95;font-style:italic;">// 删除首尾空格</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;"> 123 </span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">trim</span><span style="color:#A6ACCD;">() </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 删除首部空格</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;"> 123 </span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">trimStart</span><span style="color:#A6ACCD;">() </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">// 删除尾部空格</span></span>
<span class="line"><span style="color:#A6ACCD;">console</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">log</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;"> 123 </span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">trimEnd</span><span style="color:#A6ACCD;">() </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">---</span><span style="color:#89DDFF;">&quot;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;font-style:italic;">/*</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">---123---</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">---123 ---</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">--- 123---</span></span>
<span class="line"><span style="color:#676E95;font-style:italic;">*/</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><h3 id="_11-3-6-match-方法" tabindex="-1">11.3.6 match() 方法 <a class="header-anchor" href="#_11-3-6-match-方法" aria-hidden="true">#</a></h3><p><code>match</code>方法用于确定原字符串是否匹配某个子字符串，返回一个数组，成员为匹配的第一个字符串。如果没有找到匹配，则返回<code>null</code>。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">cat, bat, sat, fat</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">match</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">at</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;at&quot;]</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">cat, bat, sat, fat</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">match</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">xt</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// null</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>返回的数组还有<code>index</code>属性和<code>input</code>属性，分别表示匹配字符串开始的位置和原始字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> matches </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">cat, bat, sat, fat</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">match</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">at</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">matches</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">index </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"><span style="color:#A6ACCD;">matches</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">input </span><span style="color:#676E95;font-style:italic;">// &quot;cat, bat, sat, fat&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><code>match</code>方法还可以使用正则表达式作为参数，以后讲正则会说到。</p><h3 id="_11-3-7-search-方法和replace-方法" tabindex="-1">11.3.7 search() 方法和replace() 方法 <a class="header-anchor" href="#_11-3-7-search-方法和replace-方法" aria-hidden="true">#</a></h3><p><code>search</code>方法的用法基本等同于<code>match</code>，但是返回值为匹配的第一个位置。如果没有找到匹配，则返回<code>-1</code>。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">cat, bat, sat, fat</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">search</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">at</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// 1</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><code>search</code>方法还可以使用正则表达式作为参数，以后讲正则会说到。</p><p><code>replace</code>方法用于替换匹配的子字符串，一般情况下只替换第一个匹配（除非使用带有<code>g</code>修饰符的正则表达式）。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">replace</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">b</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;baa&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p><code>replace</code>方法还可以使用正则表达式作为参数，以后讲正则会说到。</p><h3 id="_11-3-8-split-方法" tabindex="-1">11.3.8 split() 方法 <a class="header-anchor" href="#_11-3-8-split-方法" aria-hidden="true">#</a></h3><p><code>split</code>方法按照给定规则分割字符串，返回一个由分割出来的子字符串组成的数组。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;b&quot;, &quot;c&quot;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如果分割规则为空字符串，则返回数组的成员是原字符串的每一个字符。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;|&quot;, &quot;b&quot;, &quot;|&quot;, &quot;c&quot;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如果省略参数，则返回数组的唯一成员就是原字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// [&quot;a|b|c&quot;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如果满足分割规则的两个部分紧邻着（即两个分割符中间没有其他字符），则返回数组之中会有一个空字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a||c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&#39;a&#39;, &#39;&#39;, &#39;c&#39;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如果满足分割规则的部分处于字符串的开头或结尾（即它的前面或后面没有其他字符），则返回数组的第一个或最后一个成员是一个空字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;&quot;, &quot;b&quot;, &quot;c&quot;]</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;b&quot;, &quot;&quot;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><code>split</code>方法还可以接受第二个参数，限定返回数组的最大成员数。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">0</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// []</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;]</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;b&quot;]</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;b&quot;, &quot;c&quot;]</span></span>
<span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a|b|c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">split</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">|</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">4</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// [&quot;a&quot;, &quot;b&quot;, &quot;c&quot;]</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>上面代码中，<code>split</code>方法的第二个参数，决定了返回数组的成员数。</p><p><code>split</code>方法还可以使用正则表达式作为参数，以后讲正则会说到。</p><h3 id="_11-3-9-concat-方法" tabindex="-1">11.3.9 concat() 方法 <a class="header-anchor" href="#_11-3-9-concat-方法" aria-hidden="true">#</a></h3><p><code>concat</code>方法用于连接两个字符串，返回一个新字符串，不改变原字符串。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">abc</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> s2 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">def</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">s1</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">concat</span><span style="color:#A6ACCD;">(s2) </span><span style="color:#676E95;font-style:italic;">// &quot;abcdef&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">s1 </span><span style="color:#676E95;font-style:italic;">// &quot;abc&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>该方法可以接受多个参数。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">concat</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">b</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">c</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">) </span><span style="color:#676E95;font-style:italic;">// &quot;abc&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如果参数不是字符串，<code>concat</code>方法会将其先转为字符串，然后再连接。</p><div class="language-js line-numbers-mode"><pre><code><span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> one </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> two </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">var</span><span style="color:#A6ACCD;"> three </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">3</span><span style="color:#89DDFF;">&#39;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#89DDFF;">&#39;&#39;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">concat</span><span style="color:#A6ACCD;">(one</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> two</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> three) </span><span style="color:#676E95;font-style:italic;">// &quot;123&quot;</span></span>
<span class="line"><span style="color:#A6ACCD;">one </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> two </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> three </span><span style="color:#676E95;font-style:italic;">// &quot;33&quot;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>上面代码中，<code>concat</code>方法将参数先转成字符串再连接，所以返回的是一个三个字符的字符串。作为对比，加号运算符在两个运算数都是数值时，不会转换类型，所以返回的是一个两个字符的字符串。</p></div></div><!----></main><!--[--><!--]--><footer class="VPContentDocFooter" data-v-4fe9b7bd data-v-7f892bef><a class="prev-link" href="/js/08.html" data-v-7f892bef><span class="desc" data-v-7f892bef><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" viewbox="0 0 24 24" class="vt-link-icon" data-v-7f892bef><path d="M15,19c-0.3,0-0.5-0.1-0.7-0.3l-6-6c-0.4-0.4-0.4-1,0-1.4l6-6c0.4-0.4,1-0.4,1.4,0s0.4,1,0,1.4L10.4,12l5.3,5.3c0.4,0.4,0.4,1,0,1.4C15.5,18.9,15.3,19,15,19z"></path></svg> Previous</span><span class="title" data-v-7f892bef>08 【标准库之Date对象】</span></a><a class="next-link" href="/js/10.html" data-v-7f892bef><span class="desc" data-v-7f892bef>Next <svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" viewbox="0 0 24 24" class="vt-link-icon" data-v-7f892bef><path d="M9,19c-0.3,0-0.5-0.1-0.7-0.3c-0.4-0.4-0.4-1,0-1.4l5.3-5.3L8.3,6.7c-0.4-0.4-0.4-1,0-1.4s1-0.4,1.4,0l6,6c0.4,0.4,0.4,1,0,1.4l-6,6C9.5,18.9,9.3,19,9,19z"></path></svg></span><span class="title" data-v-7f892bef>12.正则表达式</span></a></footer></div></div></div></div><div class="visually-hidden" aria-live="polite" data-v-23306c50>10.Math对象 has loaded</div></div></div>
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